This invention generally relates to water quality or purity indicators, and specifically to a water quality indicator which is adapted to operate on AC input power to prevent contaminant build-up on the indicator test probes.
Many of the conventional water purifying systems in use in homes or in industries are equipped with a water purity indicator which measures the purity level or level of contaminants in the water. The purity indicators provide useful information as to whether the water is fit for its intended purposes. Typically, the known purity indicators include a pair of test probes or electrodes which are connected to a circuitry, which detects contaminants in the water by measuring the electrical conductivity or resistivity of the water. This is a reliable method for determining the purity of water, since the conductivity of water is directly proportional to the quantity of ionizable dissolved solids, such as minerals, normally found in impure water. The purity level of the water is obtained by comparing the measured conductivity value with a predetermined reference conductivity value. For example, if the measured conductivity falls below the reference value, the condition of the water would be considered acceptable for its intended purposes. On the other hand, if the measured conductivity exceeds the reference value, then it would suggest that the water is contaminated to the point that it would not be acceptable for its intended purposes. Displays such as light emitting diodes (LED) are typically employed to indicate the condition of water to a user.
A common feature of the conventional water purity indicators is that they are operated by DC input power, including the current that is applied to the test probes for measuring the conductivity or resistivity of water. As a consequence, salts or dissolved minerals in the water accumulate on the probes due to electrolytic reaction, thereby degrading the accuracy of the conductivity readings.
One known method for preventing contaminant build-up on the probes is disclosed in U.S. Pat. No. 4,885,081, which is a continuation of U.S. Pat. No. 4,623,451. These patents teach solving this problem by applying a pulsating DC current to the probes or electrodes to "cancel out" the electrolytic reaction. A disadvantage of this method, however, is that an additional circuitry would have to be implemented for performing the "cancel out" process, thereby increasing the cost and the complexity of the overall circuitry of the purity indicator.
Thus, it is a first object of the present invention to provide an improved water purity indicator which prevents contaminants from coating the test probes of the purity indicator without employing additional circuitry dedicated specifically for this purpose.
It is another object of the present invention to provide an improved water purity indicator which applies an AC voltage directly to the test probes of the indicator.
Still another object of the present invention is to provide an improved water purity indicator which compares the AC voltage generated by the resistivity of water with an AC reference voltage in determining the purity of the water.